Early 2020, pre COVID
The Democrats were looking like fools between impeachment and the messy primary.
I remember polls showed Trump strongly ahead in Florida and Ohio, with states like WI and PA as tossups. Considering polls always underestimate him, Trump probably would have won a larger victory than 2016.
Let's not forget that in the very early days of the pandemic just starting Trump saw a rally-around-the-flag effect and had his most positive approval ratings ever. It didn't take long for him to f*** that up entirely shortly after though. And I think the real indicator of when Trump became defeatable was the infamous "inject disinfectant" press conference. The country was willing to give him a chance to get us through this crisis and he quickly demonstrated that he had no idea what he was doing yet again.